<!DOCTYPE html>
<html>
<head>
<style type="text/css">
.separator {
 height: 20px;
 background-color: green;
}
#min-height {
 min-height: 0;
 height: auto;
 margin-top: 20px;
 margin-bottom: 30px;
}
#margin-only-child {
 margin-top: 40px;
 margin-bottom: 10px;
}
</style>
</head>
<body>
<div class="separator"></div>
<div id="min-height">
 <div id="margin-only-child"></div>
</div>
<div class="separator"></div>
</body>
</html>
